3. Development of the urogenital system

Question 1

What structure becomes the posterior abdominal wall?

Answer 1

The mesoderm by lateral folding that enclose intra-embryonic coelom (The peritoneal cavity)

Question 2

How does the mesoderm form the peritoneal cavity and posterior abdominal wall in development?

Answer 2

1. The mesoderm forms somites adjacent to the notochord and developing neural tube.
2. These form intermediate and lateral plate mesoderm
3. The lateral plate mesoderm cavitates to form the coelom
4. Folding moves the intermediate mesoderm to the posterior abdominal wall while the coelom becomes the peritoneal cavity

Question 3

What are the two points from which urinary and reproductive systems begin development?

Answer 3

1. Mesoderm and coelomic epithelium of the posterior abdominal wall
2. Endodermally derived cloaca (divided by the urorectal septum) and the allantois

Question 4

What does the renal primordia in the mesoderml form sequentially 3 times to form?

Answer 4

The renal primordia form sequentially 3 times within the mesoderm of the posterior abdominal and pelvic walls.
Forms the pronephros, mesonephros and metanephros.

Question 5

Where do the mesonephric ducts open into?

Answer 5

The cloaca

The cloaca is being divided by the urorectal septum into:
Anteriorly: Urogenital sinus and allantois
Posterioly: Recto-anal region posteriorly

Question 6

By the 5th week, what stages is the urogenital system in development?

Answer 6

The ureteric bud (on each side) extends from the mesonephric (Wolffian) duct and induces the metanephros that is forming in the pelvis.
The metanephros will become the definitive kidney
The metanephric blastema lie adjacent to each other

Question 7

The ureteric bud gives rise to the _____ and ______ ducts
The metanephros becomes the renal tissue i.e. glomeruli and loops of _____
The kidney is functional by about __ weeks
If the collecting ducts do not meet the nephric vesicles, ____ form within the kidney

Answer 7

The ureteric bud gives rise to the ureter and collecting ducts
The metanephros becomes the renal tissue i.e. glomeruli and loops of Henle
The kidney is functional by about 10 weeks
If the collecting ducts do not meet the nephric vesicles, cysts form within the kidney

Question 8

What 2 abnormalities can occur when the kidney ascend from the pelvis up the posterior abdominal wall?

Answer 8

1. Pelvic kidney (1 risen, 1 in pelvic)

2. Horseshoe kidney (1 fused kidney in the pelvis

Question 9

What is the consequence of abnormal branching of the ureteric bud before it reaches the metanephric blastema?

Answer 9

Bifid ureter

Question 10

If the ureteric bud fail to branch at all within the metanephros, then there will be no induction of kidney development. Condition?

Answer 10

Renal agenesis

1 ureter may end up going to bladder, 1to vagina

Question 11

Ureteric bud extends from the…

Answer 11

Mesonephritic (Wolffian) duct

Question 12

The urogenital sinus will eventually form the..

Answer 12

Bladder and urethra

Question 13

Relationship between the urogenital sinus and mesonephric ducts and ureteric buds?

Answer 13

The urogenital sinus (bladder and urethra) grows and the mesonephric ducts and ureteric buds (ureters) become incorporated within its walls

Question 14

Ureteric buds eventually form the..

Answer 14

Ureters

Question 15

Eventually what happens to the mesonephric ducts?

Answer 15

The mesonephric ducts move caudally to open in to the urethra as the vas deferens and ejaculatory ducts

Question 16

From weeks 4-6 what 4 major changes to the urogenital system development occur?

Answer 16

1. The cloacal membrane “sinks” into a pit of ectoderm as the underlying mesoderm proliferates
2. The urorectal septum (mesoderm) completely separates the cloaca and becomes the perineal body
3. The cloacal membrane ruptures leaving the anal canal and UG sinus open to the exterior
4. The roof of the UG sinus is the urethral plate

Question 17

The proximal part of the UG sinus ____ ____ _____, while the allantois closes to become the ______, which may remain patent

The pelvic part of the UG sinus becomes the prostatic and membranous ____

The distal part of the endodermal UG sinus or ______ UG sinus is drawn along the floor of the extending genital tubercle as the ______ ______

Answer 17

The proximal part of the UG sinus becomes the bladder, while the allantois closes to become the urachus, which may remain patent

The pelvic part of the UG sinus becomes the prostatic and membranous urethrae

The distal part of the endodermal UG sinus or definitive UG sinus is drawn along the floor of the extending genital tubercle as the urethral plate

Question 18

Which 4 main embryological structures for the urinary system

Answer 18

The metanephros, ureteric bud, urogenital sinus and allantois

Question 19

During week 6, the ___mesonephric duct develops lateral to the mesonephric duct as an invagination from a cord of coelomic _____l cells

The mesonephric and ____mesonephric ducts form the reproductive ducts and structures, while the ____ is formed in the mesoderm of the genital ridge, which is developed from the overlying coelomic epithelium; and ____ ____ that have migrated from the yolk sac endoderm

Answer 19

During week 6, the paramesonephric duct develops lateral to the mesonephric duct as an invagination from a cord of coelomic epithelial cells

The mesonephric and paramesonephric ducts form the reproductive ducts and structures, while the gonad is formed in the mesoderm of the genital ridge, which is developed from the overlying coelomic epithelium; and germ cells that have migrated from the yolk sac endoderm

Question 20

Which cells become the cells that produce ova and sperm

Answer 20

Germ cells

Question 21

How does female and male genital development begin to differentiate?

Answer 21

Males from mesonephric
Females from paramesonephric

Absence of the Y chromosome and the SRY gene leads to female development from the paramesonephric ducts, while the mesonephric ducts degenerate (due to lack of testosterone)

At week 8!

Question 22

Mesonephric remnants found near vagina and ovary?

Answer 22

Mesonephric remnants: Gartner’s cysts near vagina or epoophoron and paroophoron near ovary

Question 23

In male genital development, the appendix epididymis is a remnant of the proximal end of?

Answer 23

The mesonephric duct

Whilst paramesonephric ducts degenerate but remain as the appendix testis and the prostatic utricle

Question 24

Female genital development:
The two __________ (Mullerian) ducts meet in the midline and fuse with each other and with the sino-____ ___ that is derived from the posterior aspect of the urogenital sinus

During months 3 to 5, the ducts zip together in a cranial direction to form the proximal vagina and the ____

Further cranially, the ducts stay separate as the ___ and ____ uterine tubes, with fimbriated ends that are open to the coelomic (peritoneal) cavity

As the ducts lift off the posterior abdominal wall they lift peritoneum as the ____ _______

The uterus and vagina may be septate and even double.

Answer 24

The two paramesonephric (Mullerian) ducts meet in the midline and fuse with each other and with the sino-vaginal bulb that is derived from the posterior aspect of the urogenital sinus

During months 3 to 5, the ducts zip together in a cranial direction to form the proximal vagina and the uterus

Further cranially, the ducts stay separate as the left and right uterine tubes, with fimbriated ends that are open to the coelomic (peritoneal) cavity

As the ducts lift off the posterior abdominal wall they lift peritoneum as the broad ligament

The uterus and vagina may be septate and even double.

Question 25

6 uterine abnormalities during development

Answer 25

1. Double uterus + double vagina (due to incorrect fusion of paramesonephric fusion)
2. Double uterus
3. Bicornate uterus
4. Separated uterus
5. Unicornate uterus
6. Cervical atresia

Question 26

As the gonads become more differentiated from the surrounding mesoderm, they remain “tethered”, cranially and caudally by what?

Answer 26

The suspensory ligament and the gubernaculum that extends to the labioscrotal folds

Question 27

How do the testis migrate from the abdominal wall to the scrum?
Name a congenital condition that results in incomplete descent?

Answer 27

The gubernaculum shrinks to draw the testis down the posterior abdominal wall to the inguinal canal, then through the canal during the 8th and 9th months, so the testis should be in the scrotum by birth

Cryptorchidism: Failure of complete descent

Question 28

What is the process in vaginalis?

If it stays open?

Answer 28

The loop of parietal peritoneum that the testis takes into the scrum.
If it stays open = Indirect inguinal hernia, hydrocele will form

Question 29

The urogenital sinus gives rise to an endodermal urethral plate (between the adjacent ectodermal plates or ridges raised by underlying mesoderm) to form the _______ _____.
In males = growing into the penis, penile ______ and scrotum
In females= Remaining as the _____, and the separate labia minora and majora

Answer 29

The urogenital sinus gives rise to an endodermal urethral plate (between the adjacent ectodermal plates or ridges raised by underlying mesoderm) to form the external genitalia.
In males = growing into the penis, penile urethra and scrotum
In females= Remaining as the clitoris, and the separate labia minora and majora

Question 30

In the male, during week 6 the urethral folds that form on either side of the urethral _____, fuse with the genital tubercle to grow with it, and create the urethral ______ between

The folds and groove stop short of the end of the ______ ______ (glans penis), but the urethral plate continues distally as a solid cord of (endodermal) cells

Answer 30

In the male, during week 6 the urethral folds that form on either side of the urethral plate, fuse with the genital tubercle to grow with it, and create the urethral groove between

The folds and groove stop short of the end of the genital tubercle (glans penis), but the urethral plate continues distally as a solid cord of (endodermal) cells

Question 31

As the penis elongates, the edges of the urethral folds move towards each other and fuse in the midline to create the penile ______
The ______ “zips-up” from proximal to distal

The solid cellular cord in the glans ______, joins the penile urethra, and also forms the external ____

Answer 31

-As the penis elongates, the edges of the urethral folds move towards each other and fuse in the midline to create the penile urethra
The urethra “zips-up” from proximal to distal

The solid cellular cord in the glans ______, joins the penile urethra, and also forms the external _____

Question 32

Male genetalia congenital abnormalities:

1. Glans hypospadias?
2. Penile hydrospadias?

Answer 32

Abnormal canalisation of the urethra in the glans causes glans hypospadias

Failure of the urethral folds to form, or to extend along the penis and fuse throughout its full length causes penile hypospadias

Question 33

What feature of the urogenital system and anal canal predisposes them to fistulae formation?

Answer 33

Their common origin